This invention relates to a note wave generator in an electronic musical instrument, in which data which varies repeatedly at the period corresponding to a desired musical tone frequency is produced and employed for reading the contents stored in a waveform memory.
Known in the art is an electronic musical instrument according to the system that in the case where the values of the sequential sample point amplitudes of a waveform stored in a waveform memory are read successively to obtain a musical tone signal or a tone source signal, a constant corresponding to the frequency of a tone to be produced is repeatedly subjected to addition, and the reading address of the waveform memory is advanced according to the numerical increase resulted from the addition. Heretofore, in the electronic musical instrument of this type, such a constant as described above is stored in a memory for each of the tones of the keyboard. Therefore, it is necessary to provide a relatively large capacity for the memory. For instance, if the number of keys is sixty-one (61), a read only memory having sixty-one (61) addresses is employed as the memory mentioned above.
Accordingly, an object of this invention is to provide a wave generator in an electronic musical instrument, in which the storing capacity of a memory adapted to store constants proportional to frequencies is reduced.
According to this invention, twelve constants proportional to the frequencies corresponding to twelve notes in one octave, for instance, are stored in a memory in advance, and out of these constants, one corresponding to a note to be produced is read out and regularly accumulated in an accumulator. The accumulation result of the accumulator is utilized as the address for reading the sequential sample point amplitude value of the waveform out of the waveform memory; however, what can be distinguished by the output itself of the accumulator is only twelve notes in one octave.
Therefore, in this invention, the bit position of the output data of the accumulator is shifted according to the information indicating the octave range of a note to be produced, and then the output data is utilized as the address in the waveform memory. More specifically, shifting the bit position of a binary data means that its value is increased to two times, four times, eight times . . . or decreased to 1/2 time, 1/4 time, 1/8 time . . . , which means that the frequency is shifted high or low by one octave, two octaves, three octave and so on. Thus, selection of the octave range can be achieved by shifting the output but position of the accumulator.